1. Field of Invention
The present invention relates to a plasma display panel that employs light emission by gas discharge.
2. Description of the Related Art
A plasma display panel (hereinafter referred to as “PDP”) has a structure where a front plate and a back plate are disposed to face each other and the peripheral parts of the plates are sealed with a sealing member. The discharge space formed between the front plate and the back plate is filled with discharge gas such as neon (Ne) and xenon (Xe).
The front plate has the following elements:                a plurality of display electrodes that are disposed on a glass substrate and include stripe-like scan electrodes and sustain electrodes;        a dielectric layer for covering the display electrodes; and        a protective layer for covering the dielectric layer.Each display electrode is formed of a transparent electrode and a metal-made bus electrode disposed on the transparent electrode.        
The back plate has the following elements:                a plurality of stripe-like address electrodes disposed on a glass substrate;        a dielectric layer for covering the address electrodes;        barrier ribs that are disposed on the dielectric layer and partition the discharge space; and        phosphor layers that are disposed on the dielectric layer between the barrier ribs and on side surfaces of the barrier ribs and emit red light, green light, and blue light.        
The front plate and back plate are disposed to face each other so that the display electrodes and the address electrodes intersect, and discharge cells are formed in the intersecting parts of the electrodes.
The discharge cells are arranged in a matrix shape. Three discharge cells having phosphor layers for emitting red light, green light, and blue light are arranged in the display electrode direction, and form a pixel for color display.
The PDP displays a color image in the following processes:                a predetermined voltage is applied between scan electrodes and address electrodes and between the scan electrodes and sustain electrodes to cause gas discharge; and        the phosphor layers are excited by ultraviolet rays generated by the gas discharge to emit light.        
Generally, the pressure of the discharge gas filled into the PDP is about 66.7 kPa (500 Torr) and is lower than the atmospheric pressure, so that pressing force acts in the direction where the front plate and back plate are mutually pressed while the barrier ribs are sandwiched between them. In a place having low atmospheric pressure, however, the pressing force becomes weak, the PDP deforms in the swelling direction, and the pressing force acting between the front plate and back plate is reduced. As a result, when a voltage pulse is applied to the address electrodes and display electrodes in lighting the PDP, the collision between the dielectric layer and barrier ribs is repeated by vibration due to a piezoelectric effect of the dielectric layer, and noise whose frequency is within an audible region of about 10 kHz occurs.
For addressing such a problem, an example is disclosed where the thickness of a sealed part in sealing the peripheral part is made greater than the interval size in an image display region and the central part of the image display region is recessed (e.g. patent document 1).
When the thickness of the sealed part is made greater than the interval in the image display region, however, a “gap” occurs between the tops of the barrier ribs and the dielectric layer especially in the peripheral part of the image display region, thereby generating crosstalk. The crosstalk is a phenomenon where a discharge cell adjacent to a discharge cell in discharge hardly lights up. This crosstalk occurs because material called priming particles (charged particles) generated by discharge comes to the adjacent discharge cell through the “gap” and hence the discharge of the discharge cell hardly occurs. Therefore, the crosstalk causes a lighting failure, and voltage applied to address electrodes or the like is required to be increased for preventing the crosstalk, disadvantageously.
[Patent document 1] Japanese Patent Unexamined Publication No. 2004-139921